U.S. Pat. No. 4,672,501 describes a circuit interrupter that utilizes an electronic trip unit to determine and act upon overcurrent conditions occurring within a protected circuit. The long time, short time and instantaneousness overcurrent conditions are electronically determined and an operating mechanism is actuated to separate the circuit breaker contacts to interrupt the circuit.
In some applications, it would be more beneficial to directly actuate the circuit breaker operating mechanism to interrupt the circuit without having to sense the circuit current and make the determination electronically before actuating the operating mechanism, especially when a short circuit condition occurs and some damage could occur to the circuit breaker contacts.
In other applications of an electronic trip unit for overcurrent determination, such as within motor control centers, supplemental fuses are used in combination with the circuit breakers to provide such short circuit protection in view of the fast interruption provided by the fuse disintegration. U.S. patent application Ser. No. 08/140,928 filed on Oct. 25, 1993 entitled "Induction Motor Protective Circuit Breaker" discloses the provision of a fast action fuse in circuit with a circuit breaker to provide enhanced short circuit protection.
One purpose of the instant invention is to provide enhanced short circuit protection to a circuit interrupter employing an electronic trip unit without requiring an additional fuse.